Such a membrane module has become known, for example, from EP 0 270, 051.
The production of the individual filter element is associated, among other things, with an annealing process, which requires maximal temperatures. This can lead to a distortion of the material, so that the filter elements are no longer linear in shape, but—to exaggerate somewhat—assume a banana shape. Also, the final dimensions of the filter elements after the complete termination of the production process are not predictable. Deviations from the nominal size can occur. If a prefabricated gasket is attached onto the terminal region of a filter element, an excessive extension of the gasket, may occur, each time depending on the outer dimension of the filter element, in some cases, while in other cases, such attachment can lead to the circumstance that the gasket is no longer sufficiently tightly seated, or is seated with play in the terminal region. Both circumstances are associated with disadvantages. In the case of excessive elongation, this will lead sooner or later to a premature failure of the gasket, and in the case of an under-dimension, leakage can occur.
In order to avoid this disadvantage, it is proposed according to EP 0 270,051 A2 to process the sealing rings in a finished manner only on the inside, and then to attach the gasket onto the terminal region of the filter element and then to finish-processing it also on the outside.
Such a process has the following disadvantage:
After a longer operation, this leads to the fatigue of the seal material. The seals are then no longer capable of function and break down. It is thus necessary to change the seals sooner or later. The seals that are to be newly finished have the correct outer size, but they must again be attached onto the filter elements and must be processed on the outside in the attached state. For this purpose, the filter elements must be dismantled individually from the membrane module. This involves a considerable expense.